JPH11142985A - Image reader - Google Patents

Abstract

PROBLEM TO BE SOLVED: To uniformize the distribution of received light quantity on the plural pixel parts of a line sensor without making the size of a device large nor changing the characteristic of an image forming lens. SOLUTION: A longitudinal luminous flux corresponding to a main scanning direction from an original 2 illuminated by a linear light source 4 and a reflector 5 is respectively reflected by a mirror 12 on a first traveling body 3, a first mirror 8 and a second mirror 9 on a second traveling body 7, and is made incident on the image forming lens 10, and image-formed on the sensor 11 by the lens 10. The mirror 12 is constituted of a planar base plate and a reflecting coat 12b formed on the surface of the base plate. The reflectance of the coat 12b is changed in the longitudinal direction of the mirror 12 so that the distribution of the received light quantity on the plural pixel parts is uniformized; therefore, light quantity correction to the line sensor can be performed without newly adding a shading correcting plate.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to an image reading apparatus, and more particularly to an image reading apparatus capable of obtaining image reading data in the state of electric signals by main-scanning an image formed by reducing an original surface. The present invention relates to an image reading device.

[0002]

2. Description of the Related Art Conventionally, an image obtained by reducing the size of an original is referred to as CC.
An image is formed on a band-shaped light receiving surface formed on a line sensor such as D, the band-shaped light receiving surface is electrically main-scanned, and at the same time, the document surface is sub-scanned to thereby obtain information on the document surface in a predetermined manner. 2. Description of the Related Art There is known an image reading apparatus that reads in the state of a digital signal. Such an image reading apparatus is widely applied to apparatuses for reading an image, such as a digital copying machine, an image scanner, and a facsimile apparatus. A conventional example in which such an image reading apparatus is used in a digital copying machine will be described with reference to FIG. In this image reading device,
A mounting plate 1 made of a transparent glass flat plate is provided, and a document 2 is mounted on the mounting plate 1 with its surface facing down.
The first traveling body 3 is disposed below the.

The first traveling body 3 is provided with a linear light source 4, a reflector 5 and a mirror 6, which are linearly formed in the main scanning direction of the original 2 (a direction perpendicular to the plane of FIG. 7). The belt-like light is efficiently emitted from the light source 4 by the reflector 5 in the main scanning direction of the original surface of the original 2. The image of the document 2 illuminated by such illumination light is 90 degrees vertically by a mirror 6 arranged at an inclination angle of 45 ° below.
After being bent backward (to the left in FIG. 7), it is incident on the second traveling body 7. The second traveling body 7 is provided with a first mirror 8 and a second mirror 9, and the luminous flux from the first traveling body 3 incident on the second traveling body 7 is disposed at an inclination angle of 45 °. A second mirror 9 disposed at an inclination angle of 45 ° after being bent 90 ° downward by the first mirror 8
Is bent forward by 90 ° to enter the imaging lens 10. A line sensor 11 is disposed at an image forming position of the image forming lens 10, and the image of the document 2 is formed by the image forming lens 10.
Is formed on the line sensor 11.

In the line sensor 11, a plurality of pixel units are arranged in a line at a predetermined pixel pitch. Then, in the line sensor 11 in which the image of the document 2 is reduced and formed into an image, a main scanning operation for sequentially obtaining outputs obtained by photoelectrically converting incident light to each of the plurality of pixel portions is performed. The first traveling body 3 is moved to the speed V1 in synchronization with the scanning operation.
And the second traveling body 7 moves rightward at half the speed V2 (FIG. 7).
The sub scanning of the original 2 is performed in a state where the optical path length from the imaging lens 10 to the original 2 is unchanged. During the sub scanning operation, the main scanning operation described above is repeated. By doing so, it is possible to obtain read data consisting of electric signals corresponding to the information of the document 2.

In such an image reading apparatus, even if the original 2 is uniformly illuminated by the linear light source 4 and the reflecting umbrella 5, the characteristics of the imaging lens 10 cause the peripheral portion of the longitudinal light beam to be illuminated. Is reduced to about the cos 4 power law of the half angle of view as compared with the light amount at the center. To this end, conventionally, a filter plate (hereinafter, referred to as a “shading correction plate”) that blocks a part of the light flux at the center is disposed closer to the document 2 than the imaging lens 10 and a plurality of pixels of the line sensor 11 are arranged. The light receiving distribution was made uniform in the section.

When such a shading correction plate is inserted on the object side of the imaging lens, the shading correction plate also functions as a member for fixing the imaging lens 10 and has a function of a shading correction plate. JP-A-3-236040
No., published in Japanese Patent Application Publication No. That is, an attachment member for fixing the imaging lens to the lens barrel is formed of a plate-shaped member, and a shading correction opening that blocks a part of light incident on the imaging lens is formed. . In this way, by using the shading correction plate and the imaging lens fixing member in common, the number of steps in the assembly process of the imaging lens and the cost can be reduced.

[0007]

In a conventional image reading apparatus, the characteristics of an image forming lens for forming an image on a plurality of pixel portions of a line sensor even if the original is uniformly illuminated by a light source. Accordingly, the light amount at the peripheral portion in the longitudinal direction of the line sensor is smaller than the light amount at the central portion by a half angle of view co.
It is reduced to about the s4 power law. Further, Japanese Patent Laid-Open No.
As described in JP-A-236040, a shading correction plate that blocks a part of the light flux at the center is disposed on the document 2 side from the imaging lens 10 so that the light reception distribution in a plurality of pixel portions of the line sensor 11 is increased. In order to uniformize the shading correction plate, the shading correction plate is required to be set apart from the imaging lens since the purpose is to block light near the axis.

For this reason, when the optical member is mechanically driven for sub-scanning while the original is fixed, the traveling body for sub-scanning cannot be moved to the vicinity of the imaging lens, and the image reading apparatus is not used. However, there is a problem that the size of the device increases. Further, in the above-described conventional apparatus, there is also a problem that the spherical aberration of the imaging lens changes to block the light flux near the axis, and the total imaging characteristic also changes. For this reason, it is necessary to design the imaging lens on the premise that the shading correction plate is inserted from the stage of designing the imaging lens. Therefore, the imaging lens can be used only for an optical system in which a predetermined shading correction plate is inserted at a predetermined position in front of the imaging lens, and a part of the optical system is redesigned and used for another device. Therefore, the versatility of the imaging lens is very low.

The present invention has been made in view of the above circumstances, and has as its object to reduce the number of line sensors without increasing the size of an image reading apparatus and without changing the characteristics of an imaging lens. It is an object of the present invention to provide an image reading apparatus capable of making the distribution of the amount of received light uniform in the pixel portion.

[0010]

In order to achieve the object of the present invention, an image reading apparatus according to the first aspect of the present invention comprises a single longitudinal light beam corresponding to the main scanning direction of a document illuminated by illumination means. The light is reflected by using the above-described longitudinal mirror, and the light beam reflected by the mirror is made incident on the imaging lens, and the imaging lens forms a plurality of pixel portions in a row in the longitudinal direction of the line sensor. In an image reading apparatus that forms an image in accordance with an axis and scans image information on the original surface by scanning a plurality of pixel units of the line sensor, a light reception distribution in the plurality of pixel units of the line sensor is uniform. In addition, the reflectance distribution on the surface on which the reflective coating formed on the mirror is formed is changed in the longitudinal direction of the mirror.

According to a second aspect of the present invention, there is provided an image reading apparatus, comprising: an image reading device configured to generate one or more longitudinal light beams corresponding to a main scanning direction of a document illuminated by an illuminating means; The light reflected by the mirror is made incident on an imaging lens, and the imaging lens is aligned with the longitudinal axis of a line sensor in which a plurality of pixel units are formed in a row. An image reading apparatus that forms an image and reads image information of the original surface by scanning a plurality of pixel units of the line sensor, comprising a cover glass that covers the plurality of pixel units of the line sensor, The transmittance distribution in the cover glass is changed in the longitudinal direction in which the plurality of pixel portions of the line sensor are formed so that the light reception distribution in the plurality of pixel portions is uniform. It is an.

[0012]

The "mirror" in the image reading apparatus according to the first aspect of the present invention has a uniform light receiving distribution in a plurality of pixel portions of the line sensor, in other words, the brightness of the original. When the distribution is uniform, the reflectance distribution on the surface on which the reflection coating is formed on the mirror is determined in such a manner that the distribution of the amount of light incident on each of the plurality of pixel portions of the line sensor becomes uniform when the distribution is uniform. Has been changed. That is, the light quantity deterioration characteristic of the imaging lens is cos4
Degradation is increasing toward the periphery in both directions with the optical axis as a boundary due to the power law, etc., so that the reflectance distribution characteristics of the mirror must be The reflectance is increased toward the periphery in both directions with the axis as a boundary.

[0013] On the other hand, the "cover glass" in the image reading apparatus according to the second aspect of the present invention is provided in the light transmitting film so that the distribution of the amount of light incident on each of the plurality of pixel portions of the line sensor becomes uniform. The transmittance distribution is changed in the longitudinal direction (main scanning direction). In other words, the light quantity deterioration characteristic of the imaging lens becomes larger as it goes to the peripheral portion in both directions with the optical axis as a boundary due to the cos 4 power law and the like, so that the light reception distribution characteristic of the line sensor becomes flat. To increase the transmittance, the transmittance distribution characteristics of the light-transmitting coating are increased toward the periphery in both directions with the optical axis as a boundary.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS First, an image reading apparatus according to a first embodiment of the present invention will be described with reference to FIGS. In this embodiment, the image reading apparatus of the present invention is applied to a digital copying machine, and there are many parts in common with the configuration and operation described in the section of the prior art with reference to FIG. Here, the common components will be denoted by the same reference numerals, and their operations will be omitted or simplified, and different portions will be mainly described. In the configuration of the image reading apparatus shown in FIG. 1, the mirror 6 in the configuration of the image reading apparatus shown in FIG. 7 is removed, and a mirror 12 is provided instead.

As shown in FIG. 2, the mirror 12 is formed by plating or depositing a metal such as aluminum on the surface of a flat glass substrate 12a having a high degree of flatness to form a reflective coating 12b. is there. The image reading apparatus converts a longitudinal light beam (a light beam formed in a band shape in the main scanning direction) corresponding to the main scanning direction of the document 2 illuminated by the illumination unit formed by the linear light source 4 and the reflector 5. The light is reflected through one or more longitudinal mirrors, that is, in this embodiment, three longitudinal mirrors of a mirror 12, a first mirror 8, and a second mirror 9, and the reflected light flux is formed into the imaging lens 1
0, and the imaging lens 10 forms an image in the main scanning direction of the line sensor 11 in which a plurality of pixel units are formed in a row, and scans the plurality of pixel units of the line sensor 11. The image information of the document 2 is read.

The mirror 12 is arranged so that the light receiving distribution in the plurality of pixel portions of the line sensor 11 is uniform, in other words, when the luminance distribution of the document 2 is uniform, each of the plurality of pixel portions of the line sensor 11 The reflectance distribution on the surface on which the reflective coating 12b is formed on the mirror 12 is adjusted so that the distribution of the amount of light incident on the mirror 12 becomes uniform.
In the longitudinal direction. More specifically, as shown in FIG. 2, which is a characteristic diagram schematically showing the relationship between the position of the mirror 12 and the reflectivity distribution, the reflectivity of the reflective film 12b is set at the end in the longitudinal direction with respect to the center O of the mirror. A reflection increasing film (for example, a metal film, a dielectric multilayer film, or the like) is applied so that the reflectance increases toward the edge.

The mirror 12 in the first embodiment
As shown in FIG. 3, the reflection distribution like the reflection characteristic C is controlled by controlling the film thickness of the reflection coating 12b so as to correct the peripheral light amount drop by the imaging lens 10, that is, the light amount deterioration characteristic a. A characteristic is provided so that the amount of light on the surface of the line sensor 11 after passing through the imaging lens 10 is made uniform. The above-described correction of the reflectance is performed according to three types of characteristics, that is, the light amount deterioration characteristic a of the imaging lens 10, the reflectance distribution characteristic b of the mirror 12, and the light reception distribution characteristic c of the line sensor 11. Means may be added to correct for uneven illumination light in the main scanning direction.

For this reason, when the main scanning light beam from the document 2 is imaged on a plurality of pixel portions of the line sensor 11, the distribution of received light in the plurality of pixel portions becomes uniform without using a shading correction plate. It is not necessary to newly provide a shading correction plate as in the related art, and the configuration can be simplified. Further, since it is not necessary to install a shading correction plate as in the related art, it is possible to move the second traveling body 7 to the vicinity of the imaging lens 10, thereby increasing the overall size of the image reading apparatus. Can be prevented.

Further, in the case of using the conventional shading correction plate, the vicinity of the light beam on the axis is blocked, whereas in the first embodiment, the reflectance of the mirror 12 is made different. Since the light reception distribution in the plurality of pixel portions of the line sensor 11 is made uniform, there is no change in spherical aberration caused by blocking the light flux near the axis of the light flux. Thus, the design performance of the imaging lens 10 can be maintained from on-axis to off-axis of the light beam.

Next, an image reading apparatus according to a second embodiment of the present invention will be described with reference to FIGS. In addition,
In the second embodiment, the image reading apparatus of the present invention is applied to a digital copying machine, and there are many parts in common with the configuration and operation described in the section of the prior art with reference to FIG. In order to avoid this, the description of the common configuration will be omitted or simplified, and the description will focus on different parts. The line sensor 13 shown in FIG.
Line sensor 11 in the configuration of the image reading apparatus shown in FIG.
Is an alternative to

As shown in FIG. 5, the line sensor 13 is formed on a surface of a substrate 13a which is a flat and long insulating substrate (ceramic plate or the like) having a high degree of flatness, and has an integrated circuit forming technology. Are formed at a predetermined pitch corresponding to a plurality of pixels (a predetermined number of pixels, for example, 400), and a cover glass made of a transparent glass material is formed on the upper surface of the pixel portion 13b. 13c is connected to the substrate 13a by an adhesive portion 13e provided in the peripheral portion. A light transmitting film 13d is formed on the surface of the cover glass 13c. Also, the first shown in FIG.
This embodiment is different from the first embodiment in that a normal mirror 12 'having a uniform reflectance over the entire surface is used as the mirror 12.

The image reading apparatus according to the second embodiment comprises a linear light source 4 and a reflector 5 as shown in FIG.
A longitudinal light beam (a light beam formed in a band shape in the main scanning direction) corresponding to the main scanning direction of the document 2 illuminated by the illuminating means formed by one or more longitudinal mirrors. In the embodiment, the light is reflected by using the mirror 12 ′, the first mirror 8, and the second mirror 9, and the reflected light beam is made incident on the imaging lens 10, whereby the plurality of pixel portions are arranged in a row. An image is formed on the line sensor 13 in a main scanning direction of the formed line sensor 11 in a state of being aligned with a longitudinal axis of the longitudinal light beam, and a plurality of pixel portions of the line sensor 13 are main-scanned. The image information of the document 2 is read.

By the way, when the line sensor 13 assumes that the light distribution in the plurality of pixel portions 13b is uniform, in other words, the luminance distribution of the document is uniform,
The transmittance distribution in the light transmitting film 13d is changed in the longitudinal direction of the line sensor 13 so that the distribution of the amount of light incident on each of the plurality of pixel portions 13b of the line sensor 13 is uniform. . Specifically, the light-transmitting coating 13d with respect to the position of the line sensor 13 in the longitudinal direction
As shown in FIG. 5, which is a characteristic diagram schematically showing the relationship between the transmittance distributions, the transmittance of the light-transmitting coating 13d is increased from the center O of the line sensor toward the peripheral portion in both end directions. Thus, the transmittance is increased.

FIG. 6 shows the light amount deterioration characteristic a of the imaging lens 10.
And the transmittance distribution characteristic b of the light transmitting film 13d formed on the cover glass 13c and the plurality of pixel portions 1 of the line sensor 13.
FIG. 9 is a characteristic diagram showing three types of light-receiving surface light amount distribution characteristics c corresponding to the angle of view (°) with respect to 3b. In other words, the light quantity deterioration characteristic a of the imaging lens 10 becomes larger as it goes toward the both edges with the optical axis O as a boundary due to the cos 4 power law or the like. In order to make the light receiving surface light amount distribution characteristic b flat, the transmittance is increased as the transmission distribution characteristic c of the light transmitting film 13d moves toward both ends with the optical axis O as a boundary. That is, a reflection increasing film (for example, a metal film, a dielectric multilayer film, etc.) is applied to a central portion of the line sensor 13 in the main scanning direction, and an anti-reflection film is applied to the peripheral portion, so that the central portion is The transmittance in the part can be increased.

With such a configuration, the main scanning light beam from the document is transmitted to the plurality of pixel portions 13 of the line sensor 13.
When the image is formed on the pixel b, the light-receiving surface light amount distribution in the plurality of pixel portions 13b becomes uniform, so that it is not necessary to newly provide a shading correction plate as in the related art, and the configuration can be simplified. In addition, since the shading correction plate is not used unlike the related art, the second traveling body 7 (see FIG. 1) can travel (move) to the vicinity of the imaging lens 10, so that the size of the main body of the image reading apparatus increases. Without having to come.

Further, conventionally, when correcting the light amount by the shading correction plate, since the vicinity of the light beam on the axis is blocked, the spherical aberration changes and the image forming performance tends to change. In the second embodiment, the distribution of received light in the plurality of pixel units when the image is formed on the plurality of pixel units 13b of the line sensor 13 is made uniform, and the light flux near the axis of the light flux is blocked. Since there is no fluctuation, there is no change in spherical aberration, and the performance at the time of designing the imaging lens can be maintained from on-axis to off-axis. In addition, the line sensor 13
Cover glass 13c is made of an anti-reflection film (light transmission film 13).
Since the part forming d) is very small, the image reading apparatus of the present invention can be provided at relatively low cost.

It should be noted that the present invention is not limited to the image reading apparatuses according to the first and second embodiments described above.
It goes without saying that various modifications can be made without departing from the scope of the invention. For example, the image reading apparatuses according to the first and second embodiments are examples in which the image reading apparatus according to the present invention is applied to a digital copying machine. However, in the apparatuses such as an image scanner and a facsimile apparatus. Can of course be applied in the same manner.

Further, the "line sensor" in the image reading apparatus according to the present invention is not limited to the case of one line or one line CCD as described above, and may be the three primary colors R.
A color line sensor composed of a three-line CCD in which R, G, and B lines corresponding to each of GB are arranged in parallel may be used. A plurality of color pixels corresponding to three primary colors may be staggered or mosaic. It is also possible to use a color-compatible line sensor arranged in a shape. Further, the apparatus to which the image reading apparatus according to the present invention can be applied is not limited to a digital copier having a fixed original document and a mechanical sub-scanning optical system as described above. The image reading device may be of the following type.

In the mirror according to the first embodiment (according to claim 1 of the present invention), one mirror is provided with a light amount correction function, but a plurality of mirrors share the function. You may. Further, the transmittance distribution of the cover glass 13c in the line sensor 13 according to the second embodiment (according to claim 2 of the present invention) is achieved by changing the transmittance distribution of the light transmitting film 13d. However, the transmittance of the cover glass 13c itself may be changed. In addition, the above-described transmittance correction is performed in accordance with the characteristic of the deterioration of the peripheral light amount of the imaging lens, but a means for performing correction in accordance with illumination light unevenness in the main scanning direction by the illumination means may be added. .

[0030]

According to the image reading apparatus of the first aspect, when the main scanning light beam from the document is imaged on the plurality of pixel portions of the line sensor, the light reception distribution in the plurality of pixel portions becomes uniform. Therefore, it is not necessary to newly provide a shading correction plate as in the related art, and the configuration can be simplified. Further, since the shading correction plate is not used as in the related art, the second traveling body can be moved to the vicinity of the imaging lens, and the size of the image reading apparatus does not increase.

Further, in the case where a conventional shading correction plate is used, the vicinity near the axis is blocked, whereas in the present invention, the light near the axis of the light beam is not blocked, so that the spherical surface is not blocked. There is no variation in aberration, and the performance at the time of designing the imaging lens can be maintained from on-axis to off-axis. According to the image reading device of the second aspect, the transmittance distribution in the cover glass covering the plurality of pixel units of the line sensor is changed in the longitudinal direction in which the plurality of pixel units of the line sensor are formed. As a result, the light receiving distribution in the plurality of pixel portions is made uniform, so that it is not necessary to newly provide a shading correction plate as in the conventional art, and the structure can be simplified. In addition, since the shading correction plate is not used unlike the related art, the second traveling body can be moved to the vicinity of the imaging lens, so that the size of the image reading apparatus does not increase.

Further, if a conventional shading correction plate is used, the vicinity of the axis is blocked, and the light flux near the axis is blocked, so that the spherical aberration changes and the imaging performance also changes. Although there was a problem, in the present invention, by changing the transmission characteristics of the cover glass, the light reception distribution in a plurality of pixel portions of the line sensor is made uniform, so that the light flux near the axis of the light flux is There is no blockage, and thus there is no variation in spherical aberration, and the design performance of the imaging lens can be maintained from on-axis to off-axis of the light beam. Further, since the correction of the light amount to the line sensor is achieved by changing the transmittance distribution, it is possible to provide an image reading apparatus at relatively low cost.

[Brief description of the drawings]

FIG. 1 is an optical path diagram showing a schematic configuration of an optical system when an image reading apparatus according to a first embodiment of the present invention is applied to a digital copying machine.

FIG. 2 is a characteristic diagram schematically showing a relationship between a mirror portion and a reflectance distribution according to the first embodiment of the present invention in FIG. 1;

FIG. 3 shows a reflection distribution characteristic of a reflection coating applied to a mirror shown in FIG. 1, a light quantity deterioration characteristic of an image forming lens, and an image formed on a line sensor by being reflected by the mirror and being formed by the image forming lens. It is a characteristic view showing the relationship of the light reception distribution characteristic of a light beam.

FIG. 4 is a characteristic diagram schematically showing a relationship between a line sensor, a longitudinal position of the line sensor, and a transmittance distribution in the image reading apparatus according to the second embodiment of the present invention.

FIG. 5 is a perspective view showing a layer formation state by partially breaking the line sensor shown in FIG. 4;

FIG. 6 shows the transmittance of a light transmitting film applied to a cover glass disposed on the front surface of the line sensor shown in FIGS. FIG. 4 is a characteristic diagram illustrating a relationship between light reception distribution characteristics of a light beam that has been imaged and transmitted through the cover glass.

FIG. 7 is an optical path diagram showing a schematic configuration of an optical system when a conventional image reading apparatus is used in a digital copying machine.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 mounting plate 2 original 3 first traveling body 4 linear light source 5 reflector 7 second traveling body 8 first mirror 9 second mirror 10 imaging lens 11 line sensor 12, 12 ′ mirror 12a glass substrate 12b reflective coating 13a Glass substrate 13b Pixel 13c Cover glass 13d Transparent coating 13e Adhesion

Claims (2)

[Claims] A longitudinal light beam corresponding to a main scanning direction of a document illuminated by an illuminating means is reflected by using at least one longitudinal mirror, and the light beam reflected by the mirror is reflected by an imaging lens. The original surface is scanned by the imaging lens to form an image along a longitudinal axis of a line sensor in which a plurality of pixel units are formed in a row, and scanning the plurality of pixel units of the line sensor. In the image reading apparatus for reading the image information, the reflectance distribution on the surface of the reflection coating formed on the mirror is determined in the longitudinal direction of the mirror so that the light reception distribution in the plurality of pixel portions of the line sensor is uniform. An image reading apparatus characterized by having been changed to: 2. A light source according to claim 1, wherein the light beam reflected by the illumination means is reflected by an image forming lens by using one or more longitudinal mirrors. The original surface is scanned by the imaging lens to form an image in accordance with the longitudinal axis of a line sensor in which a plurality of pixel units are formed in a row. The plurality of pixel units of the line sensor are scanned. An image reading apparatus for reading image information, comprising: a cover glass covering a plurality of pixel portions of the line sensor; and a transmittance in the cover glass so that a light reception distribution in the plurality of pixel portions of the line sensor is uniform. An image reading apparatus, wherein a distribution is changed in a longitudinal direction in which a plurality of pixel portions of the line sensor are formed.